A navigation grade gyroscope has a bias of less than 0.01 deg/hr and an angular random walk (ARW) of less than 0.001 deg/rt(hr). One type of gyroscope is a micro-scale disk resonator gyroscope (DRG). In the prior art this type of gyroscope does not meet the standards for navigation grade performance.
The prior art DRG designs rely on the DRG being conductive either by choosing a conductive structural material, such as doped Si, or by coating a dielectric structural material, such as fused silica, with a thin metallic layer. The control structure of the DRG for drive, sense, and tuning is usually a set of electrodes placed between the resonating rings of the DRG. In the case of a Si DRG, the ultimate performance of the gyroscope is limited by the low material quality factor (Q) of silicon, which has a Q less than 100 k. In the case of a fused silica DRG the performance has been limited by the metal coatings, with Q dropping from Q˜1e6 to Q˜200 k after a coating of only 10s of angstroms of metal. Furthermore, the tight gaps between the electrodes and vibratory structure make fabrication of a symmetric structure extremely difficult due to limitations of deep reactive ion etching (DRIE).
An example of the prior art is U.S. Pat. No. 7,040,163, which issued May 9, 2006. As shown in FIGS. 1A and 1B, this prior art relies on an internal electrode structure 108A and the electrical conductivity of the resonating structure 100. Another example of the prior art is U.S. Pat. No. 7,581,443, which issued Sep. 1, 2009, and as shown in FIG. 1C, this prior art critically depends on electrode structures 104 and 106, which are also on the resonating structure 100.
U.S. patent application Ser. No. 14/024,506, filed Sep. 11, 2013, which is incorporated herein by reference, describes a touch-free drive/sense mechanism for a small and light micro-shell, which is further described in U.S. patent application Ser. No. 13/930,769, filed Jun. 28, 2013, which is incorporated herein by reference. A DRG structure, which may be 8 mm in diameter and 125 um thick is significantly different in size and proportions than a micro-shell, which may be a 1 mm diameter hollow cylinder that is 350 um tall with a wall thickness of 2 um. Thus a DRG has 1000 times more mass than such a microshell. Due to that difference in size and mass, it is unexpected that a gradient force mechanism for drive and particularly for sense for a DRG would be sufficient to achieve navigation grade performance of such a large structure. For such a greater mass both sufficient force to drive the DRG as well as sufficient sensitivity are needed.
What is needed is a device and method to drive, sense, and tune a DRG without any electrode structures or coatings, so that a high quality factor can be achieved. The embodiments of the present disclosure answer these and other needs.